The plastron is large, gular region somewhat produced and usually notched, hind lobe deeply notched; the pectoral shields may be widely separated from each other, or from a short median suture; axillary shield very small, inguinal large.
3.
A large hole may be present between the frontal bones and the basisphenoid ( Psammophis, Coelopeltis ); the maxillary may be much abbreviated and movable vertically, as in the Viperidae; the pterygoids may taper and converge posteriorly, without any connection with the quadrate, as in the Amblycephalidae; the supratemporal may be much reduced, and wedged in between the adjacent bones of the cranium; the quadrate may be short or extremely large; the prefrontals may join in a median suture in front of the frontals; the dentary may be freely movable, and detached from the articular posteriorly.